1. Field of the Invention
This invention concerns heaters for installations to transform thermal into mechanical energy.
Such installations use at least one condensable fluid making a thermodynamic cycle comprising vapor generating means, vapor heating means, vapor condensing means and vapor using means. In particular these are fossil or nuclear power stations.
By condensable fluid is generally understood water or possibly ammonia or even any fluid whatsoever presenting itself in the vapor and liquid phases during the various values of the pressure/temperature characteristics of the thermodynamic cycle.
More particularly, the invention refers to heaters with two separate nests, one of which heats the circulating water by condensation and supercooling and the other heats a partial flow of this water by desuperheating of the steam.
2. Description of the Prior Art
In FIG. 1 of the drawing, which represents the prior art, there is shown a diagrammatic representation of two heaters 10, 20 of a conventional cycle for transformation of thermal into mechanical energy. Each heater is compartmentalized into three zones: the desuperheating zone 11, condensation zone 12 and supercooling zone 13. The water to be heated, which is the feedwater of the cycle, enters by pipe 14 into the supercooling zone 13 and subsequently passes into condensation zone 12, before crossing the desuperheating zone 11 and leaving by a pipe 15 which can be connected to the inlet of the next heater 20.
Steam enters through 16 in the desuperheating zone 11 of each heater and next passes into condensation zone 12 where all the steam is transformed into condensate. The condensate from heater 10 is mixed with the condensate extracted by pipe 17 from the supercooling zone 13 of adjacent heater 20 and is subsequently sent to its own supercooling zone 13 before being extracted in its turn by pipe 18 to an adjacent heater located upstream.
FIG. 2 is a more detailed section view of the conventional heater 10 or 20 showing at I the inlet manifold of the water to be heated and at O the outlet manifold of the water. Between these two manifolds the water passes in an assembly of heat exchanger tubes 19 generally forming a nest of tubes bent into a single or triple U (termed W) and laii out in several layers. A first section of this nest of tubes 19 is connected to the inlet manifold I and is located in a box 21 which demarcates the supercooling zone 13 filled with condensate 22 and which is fitted with a condensate outlet 18. A second section of tubes 19' is located in condensation zone 12 filled with steam from box 23 which demarcates desuperheating zone 11, in which is located the water outlet manifold O connected to the third section of tubes 19". To this box 23 is connected the steam inlet pipe 16. Heater assemblies 10 and 20 are generally mounted in a cylindrical vessel 24 closed at the ends by dished ends 25.
Complete installations of conventional heating are in particular described and shown (FIGS. 1 and 3) in patent EP No. 0032641.
So as to improve this conventional cycle, represented by FIG. 1 of the drawing, from the thermodynamic standpoint and to obtain a better efficiency of the thermal conversion, cycles or circuits as shown in FIGS. 3 and 4 of the drawing have already been proposed. In the embodiment of FIG. 3, heater 50 forming the desuperheating zone 11 is separate from heater 30 and recovers the heat of the steam which it desuperheats at a higher temperature level. Generally, it only treats a part of the total flow of the water to be heated, at least 30%, but more usually about 50%.
The embodiment of FIG. 3 has already been applied to power stations. Heaters 30, 40 and 50 are of conventional design, consisting of curved tubes connected to either a water box through a tube plate, or to two manifolds, one being the inlet one and the other the outlet one, as shown in FIG. 2. In contrast, heater 30 comprises only supercooling zone 13 and condensation zone 12. This condensation zone 12 receives some steam from heater 50 through 26, as well as the condensate from the supercooling zone of the adjacent heater 40 through 17. Heater 50 receives some steam extracted at 16 and heats in its desuperheating zone 11 part of the feedwater flow leaving heater 40. Bypass pipe XY of heater 50 is provided with a throttle 27 ensuring that the exchanger 50 receives the water flow for which it has been designed. In installations where all the feedwater flow goes through 50, 27 is a normally closed valve.
The embodiment of FIG. 4 has already been described in French patent No. 1,153,029. In this embodiment, the partial flow of the water to be heated comes from condensation zone 12 of heater 30 and is re-injected in the water pipe downstream of heater 40 or at outlet of desuperheating zone 11 of this heater 40. The partial flow can vary in this execution from 3 to 25% of the total flow of the water to be heated.
The investment cost of these two embodiments of FIGS. 3 and 4 is markedly greater than that for the embodiment of FIG. 1. Not only are the exchange surfaces greater than those of heater 10, but also vessels 24, dished ends 25 and the infrastructure are much more costly for whole of heaters 30 and 50 than for heater 10. Heaters 30 and 50 also require more space in the machine room and more connecting piping. On the other hand, the dimensions of heater 50 with tubes curved as U or W are such that it is not economically conceivable to integrate heater 50 in heater 30.
The embodiment of FIG. 4 has apparently never been applied practically because the heat data concerning heater 50' dictate very large heater dimensions including great tube lengths and, therefore, would require an excessively high investment cost, not offset by the reduction of energy consumption costs. Integration of heater 50' in heater 30 is even less conceivable in the embodiment of FIG. 4 than it is for FIG. 3.